Fischer method

Water (content) NFT 60-154 ISO/DIS 6296 ASTM D 1744 Karl Fischer Method (electrometric, alter addition of KF reagent)... 

Kaibutilate [4849-32-5] Kail-Fischer method Karl Fischer titration Karl Fischer titrations Karmex... 

Determination of Water in DMAC. DMAC is hygroscopic and precautions must be taken to minimize exposure to the atmosphere. Trace amounts of water can be deterrnined by the Kad-Fischer method. 

The deterniination of the free acid through titration and of the deterrnination of water content according to the Kad-Fischer method are also important. 

Addition of hydrogen cyanide to an aldose to form a cyanohydrin is the first step in the Kiliani-Fischer method for increasing the carbon chain of aldoses by one unit. Cyanohydrins react with Grignard reagents (see Grignard reaction) to give a-hydroxy ketones. 

Chemical tests for particular types of impurities, e.g. for peroxides in aliphatic ethers (with acidified KI), or for water in solvents (quantitatively by the Karl Fischer method, see Fieser and Fieser, Reagents for Organic Synthesis J. Wiley Sons, NY, Vol 1 pp. 353, 528, 1967, Library of Congress Catalog Card No 66-27894). 

A selection of coulometric titrations of different types is collected in Table 14.2. It may be noted that the Karl Fischer method for determining water was first developed as an amperometric titration procedure (Section 16.35), but modern instrumentation treats it as a coulometric procedure with electrolytic generation of I2. The reagents referred to in the table are generated at a platinum cathode unless otherwise indicated in the Notes. 

Direct or indirect methods may be used to determine moisture in dehydrated foods. Indirect methods must be calibrated in terms of direct methods—the most common of which are the oven, distillation, and Fischer methods. Accuracy of the direct methods is difficult to evaluate except by comparison with a chosen reference method. Several reference methods are reviewed, but none can be given an unqualified recommendation as most practical and suitable for all foods. An indirect measure of moisture is the equilibrium vapor pressure of water, which can be measured easily and accurately. Arguments are presented to show that vapor pressure may be a better index of the stability of dehydrated foods than the moisture content, which has been frequently used for this purpose. 

When the foregoing considerations are applied to the Fischer method it is rather surprising to note that the time for essentially complete removal of water is, in general, very much shorter than that required in a vacuum oven and that in many cases the particle size does not seem to be of great importance (11). Thus, for example, a 0.5-hour extrac-... 

It is extremely difficult to evaluate the accuracy of the method for different foods. Unfortunately, there are virtually no data available to compare the Fischer method with any of the reference methods described previously. One exception will be referred to later. Comparisons have been made by many investigators against other methods, but no conclusions could be drawn, because the accuracy of the reference methods was also unknown (9,11, 31). 

One example of such a comparison for several dehydrated foods against a vacuum-oven method is shown in Table IV. The data for the Fischer method are given for three different extraction times and are also shown graphically in Figure 4. The drying conditions were arbitrarily chosen to be 38 hours at 70° C. 

The data in Table IV show that, with the exception of potatoes and carrots, the vacuum-oven results do not differ by more than 0.2 or 0.3% from the results with the Fischer method when a half-hour extraction was used. In order to obtain an approximate agreement with the oven method it is necessary to extract the potatoes for about 6 hours and the carrots for less than half an hour. 

The extrapolated values together with results of the second calibration method are shown in Table V. With the exception of cabbage, agreement to better than 0.2% was found in the results of the two methods for the various foods. The proper refluxing time, for a rapid determination, was then selected from the data for the high temperature extraction shown in the last four columns in Table V. The required times varied from 5 minutes for onions and carrots to 30 minutes for celery. The shortness of these times as compared with other methods illustrates the potential usefulness of the Fischer method as a rapid control method, even though its accuracy is uncertain. 

It can probably be assumed that a satisfactory test of the accuracy of a given method would consist of a comparison of its results with those of another independent method which is different in principle. Such a comparison is available in the case of onions (16). It was found that the results by the Fischer method (Schroeder and Nair calibration) were approximately 0.2% higher than those obtained by the lyophilization procedure (21). 

The most common direct methods are the oven, the distillation, and the Fischer methods. They can be made precise by careful standardization of the experimental procedures their accuracy can be assured only by calibration against some accurate reference method. 

The extraction of water at room temperature as a procedure for the calibration of the Fischer method requires further verification, because the reagent is not specific for water. It would be desirable to compare this calibration procedure with another. In general, agreement in the results of two or more independent calibration procedures might be used as a criterion of the attainment of accuracy. 

The quantitative analysis procedure involves benz extr of TNT, water extr of AN, and taking of the A1 content as insol residue. Moisture content is detd by the Karl Fischer method described in ASTM Method E203-62, except that 8 to lOg samples are added to methanol. Specific gravity is detd by water displacement, and workmanship by visual examination... 

Ibid, E170 (Electrolytic Hygrometer Method) Ibid, E171-L to E172-L (Moisture Determination in Propellants and Explosives by Distillation Method) Ibid, E172-L to E173-L (Moisture Determination in Propellants and Explosives by the Karl Fischer Method)... 

A1 from 100%, 9.0 0.5% (6) moisture content by the Karl Fischer method, 0.5% max (7) compressive strength, by pressing to 30000psi with subsequent measurement of pellet diam and height to 0.001 inch, lOOOOpsi min (8) density, by wt and vol measurement, 1.8l4g/cc min ... 

NaOH soln and w washing, 5.0 0.5% (3) HMX (MlL-H-45444A al by subtracting the binder percent from 100%, 95.0 0.5% (4) moisture content by the Karl Fischer method, 0.1 S% max (5) granulation, both Type I and II compns, gravimetrically after w/aerosol OT washing —... 

Karl Fischer Method. See below under Specifications... 

ISO 4317 1991, Surface active agents and detergents Determination of water content—Karl Fischer method. 

Frequently, it is the bisulfite addition product that is treated with CN. This method is especially useful for aromatic aldehydes, since it avoids competition from the benzoin condensation. If desired, it is possible to hydrolyze the cyanohydrin in situ to the corresponding a-hydroxy acid. This reaction is important in the Kiliani-Fischer method of extending the carbon chain of a sugar. 

MOISTURE.dat Section 4.4 At 10 selected locations inside a dryer samples of eight tablets each were drawn to determine water content by the Karl Fischer method using MULTI, the hypothesis Ho is tested that all 10 sample means and standard deviations are indistinguishable. 

Natural gas - Determination of water by the Karl Fischer method. Also BS 3156 (10053) Environmental management systems - Specification with guidance for use. Superseded BS 7750 1994 which remains current... 

In almost all theoretical studies of AGf , it is postulated or tacitly understood that when an ion is transferred across the 0/W interface, it strips off solvated molecules completely, and hence the crystal ionic radius is usually employed for the calculation of AGfr°. Although Abraham and Liszi [17], in considering the transfer between mutually saturated solvents, were aware of the effects of hydration of ions in organic solvents in which water is quite soluble (e.g., 1-octanol, 1-pentanol, and methylisobutyl ketone), they concluded that in solvents such as NB andl,2-DCE, the solubility of water is rather small and most ions in the water-saturated solvent exist as unhydrated entities. However, even a water-immiscible organic solvent such as NB dissolves a considerable amount of water (e.g., ca. 170mM H2O in NB). In such a medium, hydrophilic ions such as Li, Na, Ca, Ba, CH, and Br are selectively solvated by water. This phenomenon has become apparent since at least 1968 by solvent extraction studies with the Karl-Fischer method [35 5]. Rais et al. [35] and Iwachido and coworkers [36-39] determined hydration numbers, i.e., the number of coextracted water molecules, for alkali and alkaline earth metal... 

Instrumental methods for the determination of water in polymeric materials often rely on heat release of water from the polymer matrix. However, in some cases (e.g. PET) the polymer is hydrolysed and a simple Karl Fischer method is then preferred. Small quantities of water (10 pg-15mg) of water in polymers (e.g. PBT, PA6, PA4.6, PC) can be determined rapidly and accurately by means of a coulometric titration after heating at 50 to 240 °C with a detection limit in the order of 20 ppm. 

After prolonged degassing of a large batch of PPG, analyses showed that its hydroxyl, unsaturation, and water contents were 0.97 meq/g, 0.033 meq/g, and 0.0035%, respectively. The hydroxyl content was determined by an acetylation method, carried out with acetic anhydride (10). The amounts of unsaturation and water were determined by the mecuric acetate and Karl Fischer methods (10), respectively. The obtained analytical results indicate that the number-average molecular weight of the dihydroxy material is 2062, provided its molecular weight is arbitrarily assumed to be twice that of the monohydroxy material, and that the mole fraction of the monohydroxy poly (propylene oxide) is 0.066. This value corresponds to a number-average functionality of 1.93 for the PPG. 

By this method the weighed dry product is dissolved in methanol and titrated with the Karl Fischer solution until the color changes from brown to yellow. The visual observation can be replaced by an ammeter, which shows an steep increase in current, when the titration is terminated (dead-stop-titration). The samples can be two to four times smaller than for the gravimetric method. To avoid the visual observation completely, iodine can be produced by electrolyzation and the water content is calculated by Coulomb s law. Such an apparatus (e. g. Fig. 1.97.1 and 1.97.2) is available commercially. The smallest amount of water to be detected by such instruments is 10 pg. Wekx and De Kleijn [1.84) showed, how the Karl Fischer method can be used directly in the vial with the dried product. The Karl... 

The Karl Fischer method is a titration to determine the water content in liquid and solid materials. The method utilizes a rather complex reaction in which the water in a sample is reacted with a solution of iodine, methanol, sulfur dioxide, and an organic base ... 

Why is an anode-cathode assembly as well as a dual-pin platinum electrode needed in the coulometric Karl Fischer method ... 

---